1. The Field of the Invention
The present invention concerns a vent valve for gas pressure regulators of the type used for the distribution of natural gas. The present invention concerns also a pressure regulator using said vent valve.
2. Relevant Technology
As is known, in the distribution of natural gas, pressure regulators are used to maintain the pressure of the delivered gas at a substantially constant value, independently of the flow rate drawn by the users.
A regulator of the above mentioned type typically comprises a containment body defining a gas flow duct, along which a movable shutter is arranged.
The containment body defines also a motorization chamber containing a membrane that divides the volume of the chamber in a first zone under the same pressure as the gas in the flow duct downstream of the shutter, and in a second zone that is under atmospheric pressure thanks to the presence of a vent hole.
Said vent hole ensures that the membrane can move freely due only to the effect of the variations in the gas pressure at the outlet of the regulator.
The membrane is associated with a preload spring that determines the delivery pressure of the regulator.
The membrane is associated with the shutter in such a way as to transfer its movements to the latter, so that the shutter increases or decreases its degree of opening depending on demand by the users.
The vent hole has a sufficiently limited cross section for the passage of the gas, in order to prevent the membrane from oscillating in the presence of sudden variations in the flow rate of the delivered gas, as a consequence of the so-called “pumping” effect, which would make the operation of the regulator unstable.
Said limited cross section of the vent hole, however, poses the drawback that it prevents any rapid movements of the membrane, which would be necessary in case of important flow rate variations, for example those caused by the start or the stop of a heating boiler.
The drawback described above can be overcome by providing the pressure regulator with a vent valve arranged in parallel with said vent hole, normally closed and configured so that it opens when the pressure in the second zone of the motorization chamber exceeds a predefined value due to a wide and rapid movement of the membrane.
Said vent valve, however, poses the drawback that it allows the gas to flow out of the regulator in case of breakage of the membrane, which can represent a risk in terms of safety, especially when the regulator is exposed to high temperatures.
It is known that in order to overcome said drawback the regulator is provided with a second safety membrane.
However, the technique just described above is not effective in the presence of temperatures that are such as to cause both membranes to collapse.
It is known that in order to overcome said drawback a vent duct is used for the purpose of placing the outlet of the vent means in communication with a zone in which a possible release of gas in the atmosphere would not generate safety risks.
The known technique just described above, however, poses the drawback of being expensive to implement, considered that it requires an additional vent duct that, among other things, can be considerably long.
A further drawback posed by the above mentioned technique lies in that the presence of the vent duct involves a pressure drop that may affect the correct operation of the vent valve.
According to a known technique that represents an alternative to the one previously described, a pressure regulator is used that is oversized compared to the needs and is provided with a membrane whose dimensions are such that the maximum gas pressure variation allowable during operation causes just a small movement of the membrane, which can be managed by means of the vent hole only, with no need to provide also a vent valve.
Also this second known technique, however, poses the drawback of being rather expensive, due to the higher cost of the oversized pressure regulator.